To be honest I think windows work better as sun traps. Even in the winter a good sunny day will make a noticeable difference to my bedroom with large south facing double glazed units.

We don't (yet) have flexible panels that would survive the abuse that curtains experience.

Vertical surfaces are not nearly as effective for the majority of cases in capturing solar radiation.

But blinds then would be perfectly fine no? They can adjust their angle and aren't flexible.

Windows have lots of obstructions that reduce the effectiveness of a solar panel.

A 10% loss is not bad, even 30% isn't too bad, because every cent counts.

Putting solar panels behind an extra layer of glass that would need to be kept pristine would be counter productive.

You don't clean your windows yearly?

The voltages involved in solar panels would create an added source of danger inside the house.

Home/Commercial battery systems like EcoFlow don't seem dangerous at all to me. I feel like the danger you're describing is minimal with the wattages you'd get from window panels.

Vertical surfaces are not nearly as effective for the majority of cases in capturing solar radiation.

I will say, I've seen compelling evidence for vertical bifacial panels. In east-west facing configurations, they generate more power when demand is greater and regular panels produce little power. They also stay cooler, so they operate more efficiently. I think it's often more cost and space efficient to have more panels installed flat to something than fewer panels installed at the theoretically best angle.